A successful hip replacement or arthroplasty procedure results, in part, from selection of prosthetic joint components that are dimensioned and positioned to closely approximate or replicate the geometry and functional characteristics of a natural, healthy hip joint. Typically, the component selection process includes a pre-operative analysis of joint images. However, it has been discovered that a valuable adjunct to image analysis is the temporary fixation of one or more provisional components to a bone or bones of interest at a stage of the arthroplasty procedure prior to permanent fixation of the prosthetic joint. The provisional components are intended to mimic certain aspects of the permanent prosthetic joint in order for a surgeon to validate measurements and to test or "try-out" several different possible component sizes and configurations. Hence, provisional components are aptly known as "trials."
In a known procedure, a trial for a femoral component is used in the following manner. The proximal end of a femur is resected and the medullary canal of the femur is reamed. A broach is inserted into the resected proximal end of the femur to provide a cavity within the bone dimensioned and contoured to receive a femoral stem. However, prior to removing the broach, a trial neck or trunnion and trial head can be secured to the broach to simulate a complete femoral stem. Normally, several neck and head trials of varying lengths and geometries are successively joined to the broach in an attempt to determine an appropriate neck length and overall femoral stem length. Once these lengths have been determined, the trial neck and head are removed from the broach and the broach is removed from the femur. Subsequently, a femoral stem of the appropriate length is selected for insertion into the cavity defined by the broach using techniques known to those skilled in the art.
Other techniques require that the broach be removed from the medullary canal to allow a trial having a stem portion to be used, in addition to a trial head and neck. For example, U.S. Pat. No. 5,100,407 discloses a system including a group of variously sized trial neck/body portions and a group of differing length trial stem portions which are mixed and matched to create a suitable trial. However, repetitive removal and insertion of successions of trial stems accompanied by successive assembly and disassembly with respect to the body can consume a lengthy and costly period of time.
Another known trial includes a stem to which a collar is secured at successive points along the length of the trial until an appropriate neck length and stem length have been ascertained. Undesirably, this type of trial induces measurement inaccuracies resulting from stem movement as the collar is repeatedly engaged with and disengaged from the stem. Additionally, as the collar is moved toward the distal end of the stem, less and less of the stem is disposed within the medullary canal, causing the trial to become increasingly unstable and rendering accurate measurements very difficult to achieve.
Other anatomical considerations can further, and undesirably, increase the number of trial components in a kit. For example, trials for long hip stems must be different for the right and left femur due to the curvature or bow of the respective femurs. In other words, a long left stem trial cannot be used in the right femur and vice versa. It is believed that a trial system consisting of numerous parts that must be selected and mated in various combinations, possibly many times, is cumbersome, unnecessarily complex which wastes surgical time, among other deficiencies.